Partial Contact Wafer Retaining Ring Apparatus

ABSTRACT

The partial contact wafer retaining ring apparatus is disclosed. For example, one disclosed embodiment provides a wafer retaining ring comprising a ring for retaining the wafer, the ring having an inner diameter surface configured to restrict lateral wafer motion, and at least one interface surface configured to interface with a polishing surface. The interface surface comprises a recessed section adjacent to the ring inner diameter, configured to preclude contact between the recessed section and the polishing surface.

BACKGROUND

Wafer polishing is often performed during semiconductor fabricationoperations to planarize the surface of the wafer between process steps.Common components of wafer polishing systems include a polishingsurface, a clamping system for holding the wafer against the polishingsurface, and a wafer retaining ring to restrict lateral motion of thewafer while it is being polished.

When polishing a wafer, it is often desired that the material removalrate be uniform across the diameter of the wafer, and that the profileof material removal be consistent between wafers. However, in light ofthe extremely small scale of modern integrated circuits, and thecorresponding accuracy and precision required in fabrication steps suchas polishing, desired levels of wafer-to-wafer reproducibility inpolishing profiles may be difficult to achieve.

SUMMARY

Accordingly, various embodiments herein related to wafer polishing aredisclosed. For example, one disclosed embodiment provides a waferretaining ring comprising a ring for retaining the wafer, the ringhaving an inner diameter surface configured to restrict lateral wafermotion, and at least one interface surface configured to interface witha polishing surface. The interface surface comprises a recessed sectionadjacent to the ring inner diameter, configured to preclude contactbetween the recessed section and the polishing surface.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an embodiment of a system for polishingwafers.

FIG. 2 shows a partial axisymmetric section view of an embodiment of asystem for polishing wafers, and illustrates a deformation of apolishing pad under a wafer edge during a polishing process.

FIG. 3 shows a partial axisymmetric section view of another embodimentof a system for polishing wafers, and illustrates a deformation of apolishing pad at a location spaced from a wafer edge during a polishingprocess.

FIG. 4 illustrates a separation between areas of the polishing surfacethat have contacted the wafer, and areas of the polishing surface thathave contacted the wafer retaining ring during a polishing process, ofthe embodiment of FIG. 3.

FIG. 5 shows a cutaway view of an embodiment of a wafer retaining ring.

FIG. 6 shows an alternate embodiment of the cutaway section of FIG.

FIG. 7 shows an alternate embodiment of the cutaway section of FIG. 1.

FIG. 8 shows an alternate embodiment of the cutaway section of FIG. 1.

FIG. 9 shows a plan view of an embodiment of a wafer retaining ring.

FIG. 10 shows a flow diagram depicting an embodiment of a method forpolishing wafers.

DETAILED DESCRIPTION

Prior to discussing the partial contact wafer retaining ring apparatus,an example use environment is described. FIG. 1 shows a block diagram ofan embodiment of a wafer polishing system 100. Wafer polishing system100 comprises a retaining ring 102, a polishing surface 104, a wafer106, and a clamping device 108. Wafer 106 is disposed within waferretaining ring 102. Retaining ring 102 is configured to move laterallywith clamping device 108. Retaining ring 102 and wafer 106 are heldagainst polishing surface 104 by clamping device 108.

Retaining ring 102 comprises any ring shaped device suitable forretaining a wafer during polishing. In one embodiment, retaining ring102 comprises a partial contact wafer retaining ring. The term “partialcontact” as used herein refers to a configuration of a retaining ring102 in which the interface surface that contacts the polishing surface104 comprises a recessed section located adjacent an inner diameter ofthe retaining ring 102, configured to preclude contact between therecessed section and the polishing surface. The partial contactretaining ring configuration is described in more detail below.

Polishing surface 104 comprises any flat surface suitable for polishinga wafer. In one embodiment, polishing surface 104 comprises a polishingpad which is affixed to a wafer polishing head.

Wafer 106 comprises any flat disc shaped object suitable for polishing.In one embodiment, wafer 106 comprises a semiconductor wafer with one ormore layers of thin film deposition product on its surface. In otherembodiments, wafer 106 may comprise a similarly shaped piece of analternate material such as glass, plastic, or metal, with or without acoating of thin film deposition product.

Clamping device 108 comprises any device suitable for urging a wafer anda wafer retaining ring against a polishing surface. In one embodiment,clamping device 108 comprises a wafer carrier head with a pressurizedbladder. In other embodiments, clamping device 108 may comprise amechanically driven rigid wafer carrier head.

During polishing, a relative lateral motion is established betweenpolishing surface 104, and clamping device 108. Retaining ring 102,which is configured to move laterally with clamping device 108,restricts the lateral motion of wafer 106. This results in a relativelateral motion also being established between wafer 106 and polishingsurface 104. In one embodiment, the relative lateral motion is anorbital motion. In some embodiments, the relative lateral motion mayalso include additional in-plane rotations or translations which aresuperimposed over the orbital motion.

When polishing a wafer, it is often desired that the material removalrate be uniform across the diameter of the wafer, and that the profileof material removal be consistent between wafers. Material removal ratesnear the edge of the wafer may be influenced when the wafer comes intocontact with areas of the polishing surface that have also contacted thewafer retaining ring, or localized surface deformations on the polishingsurface which are caused by interaction between the wafer retaining ringand the polishing surface. When either or both of these conditionsoccur, the uniformity of material removal across the diameter of thewafer, and the consistency of the material removal profile betweenwafers may be adversely affected. Additionally, areas of polishingsurface 104 that contact both wafer 106 and retaining ring 102 mayexperience different wear characteristics than areas of polishingsurface 104 that contact only wafer 106. This may lead to furtherdifficulties in achieving uniform removal profiles.

FIG. 2 shows an axisymmetric view of an embodiment of a wafer polishingsystem 100 that illustrates the above concerns. In this embodiment,wafer retaining ring 102 comprises a full contact retaining ring, andclamping device 108 comprises a pressurized bladder. The term “fullcontact” as used herein refers to a configuration of a retaining ring102 in which the interface that contacts the polishing surface 104 isdirectly adjacent to the inner diameter of the retaining ring 102. Thisis in contrast to the “partial contact” retaining ring mentioned above,in which the interface that contacts the polishing surface 104 comprisesa recessed section located adjacent an inner diameter of the retainingring 102, configured to preclude contact between the recessed sectionand the polishing surface.

Continuing with FIG. 2, the outer edge of wafer 106 is directly adjacentto the interface between wafer retaining ring 102 and polishing surface104. Because of this proximity, a localized surface deformation 110,which is present near the interface of retaining ring 102 and polishingsurface 104, may be introduced beneath the edge of wafer 106. Further, aregion of the polishing surface 104 adjacent to the inner diameter ofretaining ring 102 contacts both wafer 106 and retaining ring 102 duringpolishing. This may cause this region of the polishing surface 104 toexhibit different wear characteristics, and therefore differentpolishing characteristics, than portions of the polishing surface thatcontact only the wafer 106. As discussed above, these factors may causea variation in the material removal rate across the diameter of wafer106, and may thereby compromise overall polishing uniformity.

The use of a partial contact wafer retaining ring may reduce thepresence of such localized surface deformations near the edge of thewafer. FIGS. 3 and 4 show an axisymmetric view of an alternateembodiment of a wafer polishing system 100. In this embodiment,retaining ring 102 comprises a partial contact wafer retaining ring witha recessed section 302. Recessed section 302 provides a geometric bufferbetween the edge of wafer 106, and the area of interface betweenretaining ring 102 and wafer polishing surface 104. First referring toFIG. 3, recessed section 302 is configured such that localized surfacedeformation 110 does not come into contact with wafer 106 duringpolishing. As discussed above, contact between the wafer and localizedsurface deformations on the polishing surface which are caused byinteraction between the wafer retaining ring and the polishing surfacemay have an adverse effect on polishing uniformity. The partial contactwafer retaining ring reduces this adverse effect by precluding contactbetween the edge of the wafer and the localized surface deformations.

Next referring to FIG. 4, a relative lateral polishing motion betweenpolishing surface 104 and the interfacing surfaces of wafer retainingring 102 and wafer 106 is illustrated. Because the surfaces moverelative to each other, contact between wafer 106 and areas of polishingsurface 104 that have contacted wafer retaining ring 102 may occur if afull contact wafer retaining ring is used during polishing. In contrast,in this embodiment, recessed section 302 is configured such that wafer106 does not come into contact with any areas of polishing surface 104that have also contacted wafer retaining ring 102. This may reduce anyadverse polishing effects caused by overlapping contact between the twoareas.

Moving now to the discussion of the partial contact wafer retaining ringapparatus, FIG. 5 shows a cutaway view of one embodiment of a waferretaining ring 102, and illustrates a cross section 502 of waferretaining ring 102. Wafer retaining ring 102 comprises an inner diametersurface 504, an interface surface 506, and a recessed section 302. Innerdiameter surface 504 is located on the inner diameter of wafer retainingring 102. Interface surface 506 is located on the underside of waferretaining ring 102. Recessed section 302 is recessed from interfacesurface 506, and is immediately adjacent to inner diameter surface 504.

Wafer retaining ring 102 may be constructed of any material orcombinations of materials suitable for retaining a wafer. In oneexample, wafer retaining ring 102 is constructed entirely of a polymersuch as polyethylene terapthalate, polyetheretherketone, polyacetyl, orpolyamideimide. In other embodiments, wafer retaining ring 102 may beformed from a ceramic material such as silicon carbide, or aluminumoxide. In still other embodiments, wafer retaining ring 102 may beconstructed of a combination of ceramic and polymer materials.

Inner diameter surface 504 serves to restrict lateral motion of a wafer,and may be configured in any manner suitable for this purpose. Forexample, in one embodiment, inner diameter surface 504 comprises acontinuous cylindrical surface which is perpendicular to interfacesurface 506. In this embodiment, the vertical distance from surface 506to the top edge of inner diameter surface 504 is equal to or larger thanthe thickness of a wafer.

In another embodiment, inner diameter surface 504 is configured torestrict the lateral motion of a wafer with one or more discretesurfaces of equal or non-equal size. FIG. 6 shows an example of such anembodiment. In this example, inner diameter surface 504 comprises acylindrical surface which is interrupted at regular intervals by aseries of vertically oriented channels that span the entire verticaldistance of the surface. It will be understood that the above specifiedgeometric descriptions of inner diameter surface 104 are disclosed forthe purpose of example, and that inner diameter surface 104 may haveother suitable geometric configurations.

In yet another embodiment, inner diameter surface 504 comprises aremovable surface 510, which is configured to restrict lateral wafermotion. FIG. 7 shows one example of this embodiment. In this example,removable surface 510 is sized to cover the entire inner diametersurface of retaining ring 102. Removable surface 510 is joined to theinner diameter of retaining ring 102 through any suitable means,including but not limited to gluing, bonding, fastening, or pressfitting. Removable surface 510 may be made from any material suitablefor restraining a wafer during polishing. In one embodiment removablesurface 510 is constructed of a soft material, such as polyethyleneteraphthalate, or other suitable polymer. Such a material may help toreduce a possibility of wafer edge chipping or other such damage due tocontact between the wafer edge and the inner diameter of the retainingring. Likewise, the body of wafer retaining ring 102 is constructed of amaterial which is more resistant to wear, such as aluminum oxide. Such amaterial may help to reduce a frequency of retaining ring replacement,and therefore help to reduce system downtime.

The use of the removable surface 510 may allow the surface 510 to beremoved and replaced separately from the body 102 of the retaining ring.Further, the use of a softer material for the removable surface 510 tocontact the wafer and a harder material for the body 102 of theretaining ring may allow the removable surface 510 and the body 102 ofthe retaining ring to be serviced or replaced at different intervals,and therefore may help to save costs compared to the use of a softmaterial for the entire retaining ring.

Interface surface 506 provides an interface between wafer retaining ring102 and a wafer polishing surface, and may be configured in any mannersuitable for this purpose. For example, in one embodiment, interfacesurface 506 comprises an outermost planar surface on one side of waferretaining ring 102. In this embodiment, interface surface 506 forms acontinuous planar surface, which is perpendicular to the cylindricalaxis of wafer retaining ring 102, and which spans the radial distancebetween recessed surface 302 and the outer diameter of wafer retainingring 102. It will be understood that this embodiment is described forthe purpose of example, and that the interface surface may have anyother suitable configuration.

Recessed section 302 provides a geometric buffer between interfacesurface 506, and inner diameter surface 504. During wafer polishing,this buffer creates a separation between the outer edge of the waferbeing polished, and the inner diameter of interface surface 506. Bymaintaining this separation, it may be possible to control theinteraction between the edge of the wafer, and interface surface 506during wafer polishing. For example, the separation distance may beconfigured to preclude contact between the wafer and any portion of thepolishing surface that has come into contact with interface surface 506.In another example the separation distance may be configured to precludecontact between the wafer and localized surface deformations on thepolishing surface caused by the interaction between the wafer retainingring and the polishing surface.

Recessed section 302 may be configured in any manner suitable for theabove described purpose. For example, in one embodiment, recessedsection 302 is defined by a cylindrical recess which is concentric tothe inner diameter of wafer retaining ring 102. In this embodiment therecessed surface is approximately planar, and is parallel to interfacesurface 506. The walls of the cylinder defining the outer diameter ofrecessed section 302 are concentric with the axis of wafer retainingring 102. The depth of recessed section 302 is fixed with respect tointerface surface 506, and may have any suitable dimension. For example,in embodiments configured for use with semiconductor wafers, recessedsection 302 may have a maximum depth of one half the thickness of awafer due to the location of the bevel on such wafers. In otherembodiments, the recessed section 302 may have depths outside of thisrange, depending upon the specific configuration of the wafers for whichretaining ring 102 will be used. The radial width of recessed section302 is configured to preclude contact between the wafer and any portionof the polishing surface that has come into contact with the retainingring, and to preclude contact between the wafer and localized surfacedeformations on the polishing surface caused by the interaction betweenthe wafer retaining ring and the polishing surface.

In another embodiment, recessed section 302 comprises one or morediscrete surfaces of equal or non equal size. FIG. 8 shows an example ofthis embodiment. In this example, recessed section 302 comprises acylindrical recess which is concentric to the inner diameter or waferretaining ring 102 and which is interrupted at regular intervals by aseries of radially oriented channels which span the entire radial widthof the surface.

In yet another embodiment, recessed section 302 comprises a varieddiametric width. FIG. 9 shows one example of this embodiment. In thisexample, the outer wall of recessed section 302 is defined by anelliptically shaped boundary. It will be understood that the abovespecified descriptions of recessed section 302 are disclosed for thepurpose of example, and that recessed section 302 may have othersuitable configurations.

As described above, the embodiments of partial contact wafer retainingrings detailed herein may be used during wafer polishing to precludecontact between the wafer and any portion of the polishing surface thathas come into contact with the wafer retaining ring, and to precludecontact between the wafer and localized surface deformations on thepolishing surface caused by the interaction between the wafer retainingring and the polishing surface. FIG. 10 shows an embodiment of a method1000 for polishing a wafer. Method 1000 comprises at 1002 placing awafer on a polishing surface, then at 1004 restricting the lateralmotion of the wafer with a retaining device, and then at 1006 clampingthe wafer and retaining device against the polishing surface.

Continuing with FIG. 10, method 1000 next comprises, at 1008, polishingthe wafer such that the wafer does not contact any area of the polishingsurface that has also contacted the retaining device. Any suitablemethod for polishing the wafer in this manner may be used. For examplein one embodiment, the wafer is restrained during polishing with apartial contact wafer retaining ring that has been configured topreclude contact between the wafer and any area of the polishing surfacethat has also contacted the retaining device.

Polishing the wafer at 1008 may additionally be performed by polishingsuch the wafer such that the wafer does not come into contact with anylocalized surface deformations on the polishing surface that are causedby the interaction between the wafer retaining device and the polishingsurface. Any suitable method for polishing the wafer in this manner maybe used. For example in one embodiment, the wafer is restrained duringpolishing with a partial contact wafer retaining ring that has beenconfigured to preclude contact between the wafer and any area of thepolishing surface that has also contacted the retaining device.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The subject matter of thepresent disclosure includes all novel and nonobvious combinations andsubcombinations of the various processes, systems and configurations,and other features, functions, acts, and/or properties disclosed hereinas well as an and all equivalents thereof.

1. An apparatus for retaining a wafer during polishing, comprising: aring for retaining the wafer, said ring having an inner diameter surfaceconfigured to restrict lateral wafer motion, and at least one interfacesurface configured to interface with a polishing surface, said interfacesurface having a recessed section adjacent to the ring inner diameter,configured to preclude contact between the recessed section and thepolishing surface.
 2. The apparatus of claim 1, wherein the recessedsection is configured to preclude contact between the wafer and anyportion of the polishing surface that also contacts said interfacesurface during polishing.
 3. The apparatus of claim 1, wherein therecessed section is configured to preclude contact between the wafer andlocalized surface deformations on the polishing surface due to contactwith said interface surface during polishing.
 4. The apparatus of claim1, wherein the recessed section comprises a constant diametric width. 5.The apparatus of claim 1, wherein the recessed section comprises avarying diametric width.
 6. The apparatus of claim 1, wherein therecessed section comprises a single continuous surface.
 7. The apparatusof claim 1 wherein the recessed section comprises one or more discretesurfaces.
 8. The apparatus of claim 1, wherein the inner diametersurface and the remainder of the apparatus comprise different materials.9. The apparatus of claim 1, wherein the inner diameter surface and theinterface surface comprise different materials.
 10. The apparatus ofclaim 1, wherein the inner diameter surface comprises a removable piece.11. The apparatus of claim 1, wherein the inner diameter surfacecomprises a single continuous surface.
 12. The apparatus of claim 1,wherein the inner diameter surface comprises one or more discretesurfaces.
 13. The apparatus of claim 1, wherein the inner diametersurface is perpendicular to the interface surface.
 14. A system forpolishing wafers, comprising: a polishing surface; a ring for retainingthe wafer, said ring having an inner diameter surface for restrictinglateral wafer motion, and at least one interface surface configured tointerface with the polishing surface, said interface surface having oneor more recessed sections adjacent to the ring inner diameter,configured to preclude contact between the recessed surface and thepolishing surface; and a clamping device configured to hold the waferand retaining ring against the polishing surface.
 15. The system ofclaim 14, wherein the recessed section of the retaining ring isconfigured to preclude contact between the wafer and any portion of thepolishing surface that has also contacted said apparatus duringpolishing.
 16. The system of claim 14, wherein the recessed section ofthe retaining ring is configured to preclude contact between the waferand localized surface deformations on the polishing surface due tocontact with said apparatus during polishing.
 17. The system of claim14, wherein the inner diameter surface of the retaining ring comprises aremovable piece.
 18. A method for polishing wafers, comprising: placinga wafer on a polishing surface; restricting lateral motion of the waferwith a retaining device; clamping the wafer and retaining device againstthe polishing surface; and polishing the wafer such that the wafer doesnot contact any area of the polishing surface that has also contactedthe retaining device.
 19. The method of claim 18, further comprisingpolishing the wafer such that localized surface deformations on thepolishing surface due to contact with the retaining device do notcontact any part of the wafer.
 20. The method of claim 18, whereinrestricting lateral motion of the wafer with a retaining devicecomprises placing the wafer within a ring having an inner diametersurface for restricting lateral wafer motion, and at least one surfaceconfigured to interface with the polishing surface, said interfacesurface having one or more recessed sections adjacent to the ring innerdiameter, configured to preclude contact between the recessed surfaceand the polishing surface.
 21. The method of claim 18, furthercomprising removing and replacing the inner diameter surface of theretaining ring.